Single people who reported doing good deeds were much more likely to say that they were in a relationship the next year. They also took less time to find a partner than their non-altruistic peers.
A sense of humor is a good indicator of sexual activity, too. In one study, men whom women rated as funnier reported having more sex with more partners.
For building long-term relationships, though, researchers find over and over again that altruism is a crucial and highly desirable trait.
Psychologists have yet to pit humor head-to-head against altruism. It's also important to keep in mind that many of these studies are small, and that people often behave differently in real life than they do in a lab setting, or when responding to a survey. Especially when reporting positive experiences like charity work or sex, men may be more likely to overestimate how much they actually do those things.
And because of the way that these kinds of studies are designed, they can't say conclusively that it's altruism specifically that's attractive. It might be other traits associated with altruism, or that men attractive for other reasons might also happen to be altruistic.
But the large number of studies and the consistent findings in favor of altruism are building a pretty solid case that there are some side benefits to doing good deeds. No matter what, if you're a man seeking a woman — especially for a long-term partnership — helping others can't hurt.